text:
How are aeronautical procedures created in the US?
In creating new procedures for an airport, does someone from the FAA go to an airport, examine all their information, and choose what kind of approach/departure (for example) will be created? Or do airport officials advise the FAA (chart creators)?

Are you asking about commercial aviation, or general aviation?

I want to know the algorithm why procedures changes, and how they created, especially commercial

things don't usually change unless it's to avoid dangerous situations, these are very often revealed by accidents.

You don't mention where you are which is important as in most locations this is the responsibility of the governement (or its designated agency/contractor).  You might want to start with this FAA Division responsible for procedure development for the US.

The guidelines that they use to develop procedures are contained in FAA Order 8260.3C United States Standard for Terminal Instrument Procedures (TERPS)

does a worker go to an airport and monitors all information, and choose what kind of approach/departure (for example) will be? Or do airport workers advise regulators (charts creators)?

Yes. :)
Airport/airspace procedures are mainly created by a country's local aviation authority, so if you want an instrument approach to your private airstrip in the US you would contact AFS-420, the FAA's procedures branch, probably through someone at your local FSDO, and ask them to work with you to develop the procedure.
The Procedures people will survey the approach and design a procedure that makes sure you won't hit anything on the ground, and ensure that your procedure won't conflict with other existing procedures.
Once the procedure is designed they'll test-fly it - that's done by another group - and if everything checks out they'll publish charts for it.
Once published the FAA will periodically re-evaluate then procedure, both through flight checks and other feedback (if your new procedure is generating a lot of noise complaints for example the FAA will work with you to reduce the impact).


text:
How does the ADF null positions find where the NDB is?

I understand how it operates for the most part, although I don't understand how the null positioning works. This image below doesn't include the sense antenna that limits it to one null position, however how is the null position created? Wouldn't the signal still be received at that position, how does it become null?
Also does the null positioning tell you where the NDB is? If it's null wouldn't that mean no signal is being received so the beacon wouldn't be in that direction? Or do you find the null position, the assume it's 90 degrees from the beacon?

Short answer

Do you find the null position, then assume it's 90 degrees from the
beacon?

That's correct. For the antenna pattern shown in the question, the angle between direction of nulls and peaks is 90°. When sensing a null (or a peak) there are two possible and opposite directions for the beacon. This ambiguity has to be removed. This could be done by triangulation, with a second reading of the angle of arrival after the receiver has moved a bit, but in the modern ADF antenna this is not required, a sense antenna is added to the loop antenna to change the radiation pattern (i.e. the sensitivity vs. the transmitter relative bearing):

Radiation pattern of the loop antenna, and loop + sense antenna system (measured in a horizontal plane)
With the sense antenna, the null is at 180° of the peak, and there is no ambiguity. However the performance of the system is degraded by the sense antenna, thus usually two measures are done, without the sense antenna (for maximum accuracy) and with the sense antenna (for ambiguity removal only). See further down for the details.
The reason we prefer to sense the null direction is the signal received is fading at the larger rate near the null than it is increasing in intensity near the peak. The change being sheer near the null, sensing the null is easier and gives a better accuracy.
Details follow. I added a section about electromagnetic waves details at the end of this answer for those who are interested.

ADF principle
The ADF receiver uses a small-loop antenna (the circumference is small compared to the wavelength), which principle is to sense the magnetic field of the wave, the antenna is actually a coil with a single turn, ensuring it is unsensitive to the electric field.
This loop antenna is unusual in the sense receiving antennas generally couple with the electric field of the wave. However sensing the magnetic field is efficient at lowest frequencies and for direction finding applications.

How is the null position created?   Wouldn't the signal still be
received at that position, how does it become null?

Correct, the signal reaches the antenna with the same mean intensity, regardless of the orientation.
The loop antenna reacts to the combined result of instantaneous magnetic field at all points of the antenna. According to the law of induction, two points of the loop receiving the signal with a phase difference due to the difference of distance from the transmitter (left side below) will be at a different potential, creating a current in the conductor between these points:

ADF antenna sensing NDB magnetic field (not to scale)
On the other hand (right side), when the loop plane is normal to the direction of the wave, each point of the loop receives the magnetic field with the same intensity, no back-emf is created, no difference of potential is measured, no current circulates, this is a null.
Rate of variation of gain
We mentioned earlier the radiation pattern of an antenna, which is a representation of its relative gain according to the direction. For the loop antenna:

Radiation pattern of the loop antenna (dotted line for the vertical plane). Source
The gain is provided in decibels, which is a handy way to express a ratio, here the ratio between the intensity in the direction considered, and the maximum intensity found when varying the direction. A decibel value is the logarithm of the ratio, a logarithmic scale being more usable than a linear one when the values vary by several orders of magnitude. By principle the maximum is 0dB (100%, a ratio of 1/1) and other values are negative (less than 100%, a ratio smaller than 1/1).
When looking at the indications in green, The dip in received energy (the null) near +/- 90° is narrower than the peak near 0°/180°. This tells us about the rate of variation of the sensitivity:

Signal is maximum at 0°, but varies only by less than 2 dB (1.2x) on a range of 60° around the maximum.

Signal varies by more than 30 dB (31x) for only 30° around the minimum/null.

It means it will be more accurate to determine the direction of the null rather than the direction of the peak (which is the direction of the transmitter). This is the case of many types of antenna: Nulls are more pronounced than maximums.
Loop antenna with sense antenna
There is a problem with the loop antenna: It has a symmetrical radiation pattern, when a null is found, there are still two possible opposite bearings for the transmitter. The solution is to use an additional antenna, the sense antenna, which is an antenna with the same sensitivity regardless of the bearing. It is said to be omnidirectional and is usually coupling with the electric field.
A wave creates some current in each antenna which instantaneous amplitude is $A \sin 2 \pi f t$, where $A$ is the maximum amplitude.

In the loop $A$ depends on the antenna gain, thus varies with the transmitter bearing.

In the sense antenna $A$ is constant, regardless of the transmitter bearing. This $A$ in the sense antenna is made equal to the $A$ in the loop antenna by a trivial adjustment.

Now the polarity of the signals:

In the loop the sign is positive when the bearing is in [270..(0)..90] and negative in [90..(180)..270].

In the sense antenna the sign is always positive.

The polarity in each antenna indeed depends on how we measure the signal and can be inverted, but the important point is the polarity is inverted in the loop and constant for the sense antenna. Whatever they the actual signs, we get the same result if we sum the two signals when the loop is aligned on the transmitter bearing and $A$ is maximum:

On one side $A \sin 2 \pi f t + A \sin 2 \pi f t = 2 A \sin 2 \pi f t$

On the other side $-A \sin 2 \pi f t + A \sin 2 \pi f t = 0$

The 180° ambiguity has been removed. For other bearings, when the loop is not aligned with the transmitter, $A$ for the loop won't have the maximum value and the result will be between 0 and $2A$, a heart shape curve (cardioid):

Radiation pattern of the loop antenna combined with sense antenna
In the figure above, the red curve denotes a negative polarity (a 180° phase shift). Both the loop and sense antennas have a power peak of 0dB, they are equal. The null is now opposite to the maximum, and the maximum is +3dB, meaning twice the power of the loop alone. It is easy to determine the null direction. When the null direction has been determined, the NDB direction is the exact opposite.
The usual procedure to determine the direction is:

First find a null with the sense antenna off, because the sense antenna smooths out the null dip in the radiation pattern. This give the direction with 180° ambiguity.

Do a second but rough measure with the sense antenna on to remove the ambiguity.

Modern ADF antenna
On modern ADF, the antenna doesn't rotate to determine the direction of the NDB. Instead the antenna system is a combination of multiple fixed antennas. The signal direction of arrival is determined by sensing the time of arrival at the different individual antennas. As the time of arrival is actually difficult to determine without an accurate clock, the difference of signal phase is used, as explained in this other question:
Since modern ADF receivers don't rotate, how do they work?
A practical realization:

Source

Electromagnetic waves simply
The very common representation of an EM wave:

Electric and magnetic components of an EM wave. Source
A radio wave, synonymous for an electromagnetic field, propagates in 3D space and its electric and magnetic fields are not dissociable, they are the two sides of the same coin. The classical high-level principles behind EM waves, explaining how the loop antenna can work, are quite easy to summarize, at least in the far field, the area where they actually propagate as we know:

When a current flows in a wire, a magnetic field exists around the wire as well as an electric field. If these fields vary they creates in turn another varying magnetic/electric pair, and so on. The wave propagation is just the result of electric and magnetic fields expanding from the wire.

The condition is the first magnetic field must vary, which implies the current in the wire has to be variable, it cannot be a constant DC.

Said otherwise feeding a wire with AC automatically creates a wave. Fortunately if the wire is not tweaked to resonate at the AC frequency, the wave energy is tiny. We can use electric devices on 50/60Hz without creating significant waves because a resonant antenna for this frequency has to be 6 000km long.
Electric current in an open circuit
A NDB transmitter is an AC current generator feeding, e.g., a basic vertical dipole which length is tweaked to make it resonant, like a piano string is tweaked to produce a specific sound. You may wonder how electrons can circulate in an open circuit. The truth is they don't exactly circulate, they oscillate around a fixed position:

It's well known currents are created by the drift of electrons, but what is actually the velocity of this drift? Surprisingly it is very low: In a DC flashlight it takes about 24 hours for electrons to travel the 10 cm wire connecting the battery to the LED. It's exactly like water traveling from the pumping station to the kitchen.

An antenna can be seen as a capacitor, mutual capacitance effects exist between the two elements of the antenna. Electrical loads can move on a small distance without leaving the conductor, increasing a bit the local loads density, said otherwise the wire can store some energy at different locations.

If the antenna is fed with AC, electrical loads are moved back to their initial location after half a cycle, and are pushed in the opposite direction during the next half cycle, their mean position is constant. Electrons oscillate in the open circuit without leaving it, still an AC current is created.

Wave propagation
When a current is created in an antenna, the propagation of the wave can be described by the laws of electromagnetism:

Ampère-Maxwell's law says 1/ a sinusoidal current creates a magnetic field around the antenna (Ampère's initial idea). The field intensity follows the variation of the current, 2/ the same happens with an electric field instead of a current (Maxwell addition).

Faraday's law of induction says a varying magnetic field creates an electric field. This field opposes the magnetic flux which created it according to Lenz's law. Lenz's law is to electric field what inertia is to mass (and therefore links both fields like mass is linked to inertia).

When a magnetic field varies a variable electric field is generated and when an electric field varies a variable magnetic field is generated. This leads to an infinite process:

Source: Wikipedia.
The energy of the electric field comes from the magnetic field, as postulated in Lenz's law: The electric field opposes the magnetic field changes, therefore it is a force, aka the back electromotive force (back-emf).
The wire (antenna) is only required to accelerate electrons and generate the initial magnetic field. The subsequent expanding magnetic fields are strictly due to electric fields, electrons and conductors play no role:
The two fields, normal to each other, are the two inseparable aspects of the electromagnetic field. They exist at the same time, and the repeating process leads to their propagation as wave. As fields have no mass, they can travel at the speed of light.
The wave crosses conductors while expanding. A conductor acts as a reception antenna. Depending on the conductor ability to couple more or less strongly with the electric and/or magnetic fields, a given portion of the energy from the fields is converted back into current, by virtue of the same reversible laws.

What a great upgrade of your answer mins! I would like to upvote it once more, but that's not allowed unfortunately. Oh wait...

Perhaps I am an expert in the area of surveillance, but in the field of navigation and antenna design I am not. You clearly put a lot of effort in writing this answer; it's well structured and contains a lot of well researched background information. I enjoyed reading it and I learned something new. It's answers like this that make aviation.stackexchange great. Thank you!

Let us continue this discussion in chat.

@mins I finally got it, after so many years. Thanks a million. Thanks a million for making so much effort for trying to make me understand.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
How would I go about finding stall/loiter speed data?
I have a list of 6 fixed-wing and 2 tilt-rotor aircraft that I require the stall and loiter speeds for, however I have great trouble finding these. Is there a book or website that has an extensive list of aircraft and these kinds of statistics, or a method of calculating stall speeds?
Preferably your suggestions could be used in an science paper or cited directly. But any suggestion is welcome at this point.
If you are interested the list of aircraft are:
Leonardo:        AW609;
BellBoeing:      V-22 Osprey;
Beechcraft:      King Air B200;
Piper:           PA-31;
Lockheed Martin: HC-130J;
Airbus Military: HC-144;
Airbus:          CC-295;
Lockheed Martin: CC-130H;

No airplane has one single stall speed. It depends on configuration, load, etc. You can find various stall speeds in the PoH or on placards in the cockpit itself (at a minimum, you'll find the clean configuration at max gross weight stall speed, and the flaps-down at max gross weight stall speed). There's no such thing as "loiter speed", you can circle a point at any speed between stall speed and Vne. Perhaps you meant best endurance speed? Some airplanes may have that in their PoH as well, but it's not required.

With some care you might find pilot handbooks of these aircraft. Even for military machines (e.g. Ah-64 apache) have I seen these published. However the aw609 for example is so new, that you might have trouble finding such numbers

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What’s the setting range altimeters can handle?
What’s the setting range altimeters can handle? Is there a standard requiring a certain range for aircraft to be certified? Are there many occasions where a QNH is so high or low that airplanes have problems handling that?

Do you mean the range for the reference pressure allowed in the Kollsman window?

Or do you simply mean the certified altitude range of an altimeter?

Your question is confusing (as indicated by the above two answers) because there is no such thing as a "QNH Range".  QNH is simply a converted pressure setting. There is no "range", as specifically applied to QNH.

@mins yes, exactly, I meant the reference pressure. sorry for the confusion

I edited your question accordingly. Probably the answer is in "Pressure Altimeter Systems", SAE AS8009C, if someone with the document can confirm. I wouldn't be surprised the range is 28.1 in to 30.99 in as mentioned in SAE AS392C, related to sensitive altimeters.

@mins AS8009C is a Pressure Altitude System. Those are "blind encoders" that output pressure altitude only to connect to a transponder. They do not have any baro compensation capability. Baro compensation is what defines sensitive altimeters (AS392C), and is a capability of Air Data Computers (AS8002A).

@Gerry, TSO C10b was updated to rev C (2016), which now references AS8009C instead of AS392C.

There are actually multiple different answers depending on the specific type of altimeter system and what standard applies.
The stand-alone altimeters in older aircraft and small GA aircraft (panel mounted "steam gauge") are certificated to SAE AS392C, Altimeter, Pressure Actuated Sensitive Type. The specified scale range is "at least 28.1 - 30.99 inches of Hg (946 - 1049 millibars)".
This standard was updated in 2016 to require compliance with SAE AS8009C, Pressure Altitude Systems. Altimeters built to this standard have a specified range of 27.50 - 31.50 inches of Hg (931.3 to 1066.7 mb).
Aircraft with "glass cockpits" use Air Data Computers certificated to SAE AS8002A, AIR DATA COMPUTER - MINIMUM PERFORMANCE STANDARD. Barometric corrected altitude correction is covered by Table 2, which defines a range of 22.00 - 30.98 inches of Hg or 745 - 1049 millibars.

Do Air Data Computers (TSO C106 / SAE AS8002) actually use the whole range defined in table 2? The ones I have experience with only do 28.00 to 31.00

@selectstriker2 Thanks for the note on AS8009C.  I've updated the answer. The ADCs I've seen will handle a baro input over the whole range. But looking around, I find the BARO setting control panels are OEM defined parts and don't use the full range (where I was able to find the range) so your experience is accurate for those aircraft.

+1: Interesting answer, what about the second question (QNH not in the setting range). I read Denver is way below 27.5 (24/25) in Hg.

@mins, I doubt any place is often at QNH below 27.5 as that basically means a hurricane or a very severe storm. And QFE —which Denver does have 24–25—is not used in the USA. Which leaves the question about places where they do regularly use QFE.

@mins  QNH setting adjusts to MSL, so Denver is still in the range for the baro setting. To set it to display QFE in Denver you would need an ADC that allows settings in the 24-25 inch range. I have seen NOTAMs that prohibited that enforced the FAR 91.144 restrictions 2NinerRomeo mentioned.

Yes of course, you're right.

The pressure ranges for altimeters in the United States are set forth in a technical standing order.  For example TSO-C10b in turn references SAE standard AS392C, which indicates the following performance parameters:
Type I : range to 35,000 feet
Type II: range to 50,000 feet
Both adjustable from 28.1 to 30.99 inHg.
These parameters have regulatory consequences, notably FAR 91.144, which restricts flight operations when the barometric pressure exceeds the upper limit set in the TSO.  I have found no regulation for the bottom end, I suppose because the weather would be discouragingly foul.

It is very dependent on the type of altimeter. A lot of standard GA altimeters are rated from -15,000ft to 50,000ft based on a mechanical range rather than a pressure limitation.
For example, on an older model of an aircraft from 1979 a barometer reading of 25.69 was taken from the aircrafts altimeter. At uncorrected station pressure, this would be 71,000ft.
Thus altimeter limits are altitude based, not pressure based*
*In most cases.

The question is about the setting range (the value the reference pressure can take), not the altimeter range.


text:
What types of fuel quantity sensors are used in an aircraft? How do they work?
Can you explain the different types of fuel quantity sensors used in most recent aircraft?
Are ultrasonic tank sensors used these days? How does an ultrasonic sensor work?

From this PPRune forum thread, the Boeing 777 does use ultrasonic sensors (some 20 per tank)

This airplane has some 20 sensors per tank. Each of these is effectively a "radio doppler" and works on the same principle. The sensor calculates the height of fluid by measuring the difference in the speed of the sonic signal sent out thru one sensor to another,as against the ACTUAL local speed of sound (which is a preset value) thru standard temp air.This difference is then converted very accurately into height in the tank in mm.Which translates into quantity of fuel AT THAT sensor given the actual specific gravity of fuel at that point.
  - King on a Wing

In small aircraft, fuel is measured simply with a floating fuel gauge. In large commercial aircraft, this is accomplished by measuring the capacitance of the fuel.
Ultrasonic fuel sensors seem to be prevalent in stationery ground fuel tanks, not in aircraft.

This is interesting information, but doesn't really address the question of how they work.

It's a partial answer @DanHulme, the question asks about the different types of quantity sensors used.

Basically this type of sensor is not used in aircraft. I hope this clarifies things. Hard to explain, if they are not in use. It like asking how control surface work on cars.

@mike From what i know B777 uses ultrasonic fuel sensors. Capacitance types arent used anymore

Ultrasonic fuel sensors use a transmitter/receiver to transmit a sonic pulse inside a pipe filled with fuel. The pulse is reflected back to the transmitter/receiver by the fuel surface and the time taken by the pulse is the measurement of fuel height which is then converted to fuel quantity using the fuel density and specific gravity.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
What is the difference between single and dual annular combustor?
CFM56 uses single annular and GEnX uses dual annular combustion chamber. somebody please explain with pics.

Here's an engine with old combustor cans:

Here's a single annular combustor:

And in cross section:

And now here's a dual annular combustor (DAC)  (pic from here) in cross section:

See how it's like one ring (or donut)  inside another ring.
Wikipedia states "like an annular combustor, the DAC is a continuous ring without separate combustion zones around the radius. The difference is that the combustor has two combustion zones around the ring; a pilot zone and a main zone. The pilot zone acts like that of a single annular combustor, and is the only zone operating at low power levels. At high power levels, the main zone is used as well, increasing air and mass flow through the combustor."


text:
How does the wheel speed sensor in a Boeing 777-300ER work?
I do have a maintenance manual that I found on Internet, but it doesn't have anything about the wheel speed transducer.
Any pics along with the information would be helpful.

From this Aviation Studies project report of group 2A2I at the University of applied Sciences in Amsterdam, for a Boeing 777-200:

Every wheel is equipped with an anti-skid transducer (appendix VII),
  which is installed in the axle. The transducer consists of a rotor and
  stator. According to the speed of rotation, an electrical signal is
  send to the BSCU.
This computer compares the rotation speed of all the
  wheels and detects when a wheel is rotating slower than the other
  wheels on the MLG. The BSCU will send a signal to reduce braking power
  when the rotation speed of one wheel reduces more in comparison to
  other wheels.

The principle is the wheel axle drives a permanent magnet within a 3-phase winding. The frequency of the signal generated is proportional to the wheel angular speed.
From B777 General Familiarization Manual:

Antiskid and Autobrake Diagram, source
Note: I initially believed the tacho-generator was a Socitec ST80, the same than on A320 (part number is C20105000). However when I wanted to provide a supporting document, I couldn't. So please take this as an assumption only until someone provides the part number from a Boeing document (I don't think there would be a big difference between B777 and A320 tacho-generator anyway).

Tacho-generator, part C20105000, source
More information: Bodet Aero. According to Bodet Aero, their tachometer equips A300, A310, A319, A320, A321, A330 and A340.
More about tachometers: TheAirlinePilots (section "Three Phase AC Electrical Tachometer").
This is a typical installation of the transducer (not a particular aircraft):

Source

I know how a tachogeneartor operates and thought B777 uses one too but my supervisor said Tachogenerators aren't used in any latest aircraft, they use an auto transformer to do the same.

An additional search shows that these transducers are made by Crane/Hydro-Aire, and have part nr 140-025-1, 140-025-2, 140-025100 and 140-025101. But no details on the technology used.


text:
What is the best way to align with centerline on final, rudder or slip?
Like many student pilots, I consistently find myself slightly left of centerline in the last few seconds before touchdown (e.g. between crossing the threshold, through roundout and flare), despite flying a stabilized, on-course approach on Final, with no crosswind component.
My question is how to realign with centerline in those last few seconds? I've been suggested two techniques (see below), but I'm not at ease with them.
I did see the "Crosswind, crab or slip?" question, but I believe mine is different. I am wondering what is the correct technique without crosswind. Even if they have the same answer, it's not necessarily the same question, as the technique one uses MAY be different w/crosswind (or not! I don't know).

My CFI suggested imagining the centerline extending vertically into the air, and using rudder pedals to align with it as if I was 'taxiing' on that centerline. So if the plane is to the left of this imaginary centerline, apply right pedal to yaw the aircraft to the right, and vice-versa. In either case, the longitudinal axis of the aircraft is intersecting the vertical centerline at some point down the runway.

Problem is, when I do this, it doesn't feel like the plane moves towards centerline at an appreciable rate. It just feels yawed, but without any "movement" towards the side that I'm pointing to.

Alternatively, I've seen in some videos online to use the rudder pedals to align the longitudinal axis of the aircraft PARALLEL to the vertical centerline, and instead use ailerons to slip back to centerline. So if the plane is to the left of center, point the nose of the aircraft parallel to centerline, but roll aircraft to the right.

Both unnerve me a bit, but for different reasons. For the former, I'm not used to the 'crabbed' orientation so close to the ground. For the latter, I'd prefer the wings to be level so close to the ground.
Which technique is preferable?

Possible duplicate of On crosswind landings, is it preferable to side slip or crab on final approach? Welcome to aviation.SE! I hope the other question I linked to has the answer you want, but if not please feel free to edit your question further so we can understand the difference between the two.

Edited my question. I am specifying that there is NO crosswind. What is the correct technique? Does it vary based on crosswind?

@ConwayYao, I teach the same method, outlined below, to my students whether there is a crosswind or not.  It works either way.  As the student gains more skill other methods can be taught, but I start with what provides good results in all conditions.  The exceptions come in, for example with airplane limitations, such as Cessnas with avoid slips with flaps fully extended placarding.  Then I give the student (usually a PP by then) some other tools.

Your method #2 is consistent with current FAA doctrine, and when practiced yields acceptable results.
Rudder for longitudinal axis alignment (parallel) with the centerline.
Aileron for drift.
Have a stable approach, and maintain vigilance of both inputs when on low final.  If you practice the technique for your entire final approach, you get extra practice time, and may master the technique faster.
FAA has a publication, On Landings I  (and also a II and III publication) which are all great at describing the technique.  Every student should have a copy for review.  FAA-8740-48  a copy is here: https://www.flyingd.net/documents/on-landings-part-i.pdf
To answer a comment...if you are left of the centerline, and there is no wind, and your approach is stable, then you need some right aileron to get your longitudinal axis over the centerline, and you will have to adjust your rudder while maneuvering, to keep the longitudinal axis aligned and at least parallel to the centerline.
Drift with aileron, alignment with rudder. Constantly modifying input to get the desired drift and alignment.
Aileron for drift.
Rudder for alignment.
Pitch for airspeed.
Power for altitude.

The techniques you mention only work if you are already on the centerline. If you come off the centerline you will have to correct with bank. Rudder may stop the drift away from the centerline but it alone can't really get you realigned. If you are close to the threshold and not aligned, you should not be afraid to go-around.
So why are you off centerline if you've been flying a nice stabilised approach in benign conditions? You shouldn't need to make significant last minute adjustments, you should be able to plant it on the line.
I am guessing that you're doing what I and many other student pilots have done. You start realising that the ground is getting awfully close and you're going to have to do something about it. Because you're now preparing for the flare, you don't have the 'mental capacity' to remain so focused on the lateral path, so you unconsciously let the aircraft drift. It's very subtle, so you probably haven't noticed your inattention.
A student pilot on their first flight is using perhaps 90% of their mental capacity on just controlling the thing. Adding something like radio calls will push them over 100%. But as they get used to it, that percentage required for control lowers, and they can introduce radio calls, and eventually things like navigation and instrument flying.
With practice you will eventually be able to land nice and softly and on the centerline with your eyes closed (ok maybe not literally, but...). To speed that process up you just need to be disciplined - make sure your bum is on the imaginary centerline from a long way out and keep it there, no excuses. Keep your landing point on the one place in the windscreen, and be vigilant with your speed control. Most importantly, fly the aircraft all the way to the ground. The more you practice whilst focusing on those things, the sooner you will nail your landings.

Yeah, that fixation/stress is part of it. I'm now a PPL with a couple dozen more hours under my belt since I posted this question. One thing I learned is that my brain is tricked by a visual illusion when I'm on short final. From a distance, it appears that I'm on centerline, but as I get closer, I realize I'm actually left of centerline. I've learned that it's a pure visual illusion, because one time I flew (with my CFI) from the RIGHT seat, and lo and behold, I was RIGHT of centerline. To correct, now I consciously aim just a bit right of centerline on final, and I end up perfect :)

In fact, I'm not the only one with this illusion! I found this guy on Youtube who even made a video of the same effect: https://youtu.be/SEjNi1vPbuA

Probably the best solution is to visualize the runway centerline extending out from the departure end out to infinity and focusing on flying parallel to this.  If there is a crosswind component, it can sometimes be helpful to establish the airplane in a cross controlled slip per typical crosswind landing techniques long before touchdown, using rudder input to keep the nose parallel to this imagined infinite runway centerline and aileron inputs to hold the aircraft's flight path on the centerline.  Alternatively you can fly a crabbed final approach, if you have a good intuition about the airplane's true flightpath and that it is aligned with the centerline, then cross control at flare so you upwind main landing gear makes contact with the runway first.  This style of crosswind landing requires a little more precision on your part as you have to be master of where the aircraft will go when you establish the slip in the flare.   Don't rush a precision landing; if you need a little more time to align the aircraft with centerline correctly, extend you downwind leg a little more.
If you are concerned about scraping a wingtip in the roundout slip, first choose your runways based on surface winds for the lowest crosswind component, and do NOT exceed the maximum demonstrated crosswind component listed in the Airplane Flight Manual.  Second, take a moment to observe the airplane while it's sitting on the ramp and note the approximate roll angle the A/C would have to exceed to be in danger of wingtip rash; for most high wing trainers like C152s and C172s, this angle is pretty great, probably will over thirty degrees.  Therefore don't attempt to land if it requires a roll correction greater than about 20 degrees.  Remember, you have engine power, you have gas onboard, therefore you have time and you have options; YOU CAN ALWAYS GO AROUND.

I appreciate the suggestions! But let's say there's NO crosswind or wind of any kind. I'm left of centerline (let's say by 10 feet) nearing the threshold. What do I do, yaw to the right, or stay parallel to the runway, but dip my right wing?

If there's not crosswind present, fly that runway centerline to infinity all the way to touchdown.  If you are off centerline, you are allowing the airplane to drift off centerline.  you might be unconsciously applying aileron or rudder input which are causing this.  Be more attentive on short final and be ready to correct if you find the airplane drifting off centerline.

Always to the left in no wind landings?  Perhaps you are 'aiming' on a line from your nose across the point of the spinner at the centerline.  Try looking way down the runway at the centerline.  This will also help for your flare.

If you are flying parallel to the runway centerline, (your ground track is parallel but offset from the centerline), but wish to move the aircraft laterally over to the centerline, you have to:
1. TURN the aircraft to change it's ground track to intercept the centerline, and then,
2. When the aircraft has moved laterally over to the centerline, ( or just prior to arriving at the centerline), you have to TURN the aircraft back the other way to change it's ground track to be again parallel with the centerline, so you won't overshoot the centerline and end up on the other side.
There are two ways you can turn the aircraft (change it's ground track). First, you can do it just like you would at altitude, establish a slight bank and hold it until the ground track has changed sufficiently to establish the desired lateral movement, and then roll wings level, or second, you can yaw the aircraft to create sufficient sideslip to establish the desired  rate of turn.  Bank angle will do the job faster and more efficiently. The wings generate much more aerodynamic force than the side of the fuselage. That's why it only takes a small opposite bank angle to counteract the turn rate established by almost full rudder when cross controlling in a slip.


text:
How is the flight of a tricopter controlled?
For a quadcopter, diagonally opposite rotors have the same speed and direction which causes it to hover, and adjusting the speed of the rotors give the three basic movements of a flying object, i.e. pitch, roll, yaw.
Similarly, what is the physics behind the tricopter flight control?

There are few examples of three-rotor helicopters. On of them is the Cierva W.1 Air Horse. According to Wikipedia, torque balance, and hence, yaw control
'was provided by slightly inclining each rotor axis to generate horizontal thrust components to provide anti-torque moments. The three rotor configuration was foreseen by Belgian helicopter experimenter Nicolas Florine in his patent of 1926 which presented the aforementioned means for balancing the reaction on the fuselage of two or more torque driven lifting rotors turning in the same direction.'
https://en.wikipedia.org/wiki/Cierva_Air_Horse
Pitch and roll control was obtained by regulating the lift of the rotors.
https://www.flightglobal.com/pdfarchive/view/1948/1948%20-%202048.html


text:
How many Angle of Attack sensor vanes should a commercial passenger airliner have?
The ill fated MAX of recent news had 2 angle of attack vanes, with the MCAS computer picking the worst one.
It seems a "software patch"  may not be the only improvement option available.   Sensible engineering may suggest that a minimum of three, possibly 5, or even 7 vanes would enable writing a subroutine to reject "outliers" and use an Average AOA within an acceptable Standard Deviation.
Could more AOA sensor vanes, at various locations on the aircraft, be added to this design?

The question in the title is sensible, understandable etc and (potentially) answerable from regulation. The majority of the body is rambling about something else, and then the question(s) towards the end are completely different to what is asked in the subject. Could you clarify this all a bit and perhaps remove the information which is unrelated to the question.

The question in the title is sensible, but redundant with https://aviation.stackexchange.com/q/61144/17780

Its just a distraction. If I'm asking how to bake a cake, should I specify what I had for tea, what I'm doing a week next tuesday or what time I'll be home from work? No. Probably not. Similarly, if youre asking about AoA vanes, we dont need to know your opinion on how you think MCAS worked (your opinion, mostly wrong) how computers work or how humans react to changing environments!

The description of your question MUST focus on the specific problem asked. As is, except for the second paragraph, it is just a comment to convey your opinion about the MCAS, which is not relevant and blur your real question. Thus I'm tempted to tag this question as unclear.

Ok, Ive gone ahead and put this on hold this as unclear after 3 other votes. Please specify what you are actually asking, and remove the of-topic bumpff and flag for mod attention if you want it re-opened.

Wow! A simple flow diagram shows the AOA sensor vane inputs connected to MCAS logic.  The logic flow could be programmed in BASIC, including the math calculations, rejection of outliers and response.  Unfortunately, non-constructive emotional responses are preventing proper examination of a very relevant issue.  The question is:  ARE 2 ANGLE OF ATTACK VANES ENOUGH.  The remainder is some rational why 2 may not be enough.  WHAT DO YOU THINK!.

The problem was that MCAS only took the signal from the left.  They did this because someone in their risk assessment organization classified the failure mode of loss of input as "major" instead of "hazardous" to justify one input.  The motive would be to improve dispatch reliability (two is less reliable than one if you must have both for normal function), and ease cert.

@John K  I want to make it clear this is not to BLAME, only to move forward with a better aircraft.  Putting a few more AOA sensors on there should not be a major problem, as automated flight is analogous to flying blindfolded with limited instructions on what to do.

@bogl your answer 17780 was very good.  Notice 2 sensors with pilot intervention does not quite apply here.  Also, amazingly, adding more sensors and averaging is one of the easiest fixes!

They didn't need to add more sensors.  All they had to do is take a signal off both existing ones, and configure the sytem disable MCAS, with a fault message, where there was a miscompare or loss of signal.  Notwithstanding all the other creepy crawlies that have emerged from under the rock in the investigation, had they done that none of this whole mess would've happened in the first place.

@John K well, flipping over rocks are what researchers do, starting with that wing, and those engines.  This is solvable, and the company can do it.  I would recommend the engineers start by looking at what light R/C Extra 300s with outsized control surfaces can do, and realize a heavy aircraft with a finicky wing is on the other side of the spectrum.  If human pilots cannot respond in time to prevent stalling, then then automation must be better. Another creepy crawlie would be controlled airspace routes these planes are required to fly, but a regional could be more robust.

@RobertDiGiovanni That level of redesign would have killed the project. And it wasn't really necessary. If they had gone with dual AOA input sources,a simple wiring architecture/software issue, where a miscomp or loss triggered a fault message, disabled MCAS with maybe an appropriate flight envelope restriction via QRH,none of this would've happened and MCAS would've been merrily doing its thing,and AOA problems would've been a no more than a maintenance/dispatch reliability headache.Of course a dedicated QRH or flight restriction would've probably impacted the 737 type status and round we go.

MCAS, with further work, may have a future.  Would I love to be on that engineering team (its been a while)!! I would start at 5 degrees, where the supercrit L/D peaks, rather than at 12 degrees near stall.  The computers can really help, as long as the sensors are reliable and the software is on the same page.  Best of luck returning soon for this one.

This depends very much on what the AOA sensors are used for.
Traditional airplanes
Traditionally, AOA sensors are only used for stall warning and stall barrier (i.e. stick pusher). In this case, you can get away with only two AOA sensors. A sensible design would trigger the pilot/copilot side stall warning with the onside (or opposite side) AOA sensor, which would confer the largest availability on stall warning. This is sensible because traditional stall warning does not effect flight controls and a nuissance stall warning can be inhibited manually by the flight crew.
Stick pusher, on the other hand, should require more prudence. By regulation, the activation of the stick pusher must be beyond the stall warning activation; and the airplane is designed to be stall-free if appropriate actions are taken from the recognition of stall warning activation. Therefore, the use of stick pusher is beyond the operational envelope of the airplane. A sensible design would be to require both AOA sensors to be functional and agree for the stick pusher to activate.
Fly-by-wire airplanes
For FBW or even partial FBW airplanes, AOA information is often directly in the loop of flight controls for gain scheduling and envelope protection (e.g. MCAS). This becomes a completely different problem. By regulation, continued safe flight and landing must be possible without exceptional pilot skills following any single point failure in any flight control related system.
This would require at least three AOA sensors for these airplanes. It's not enough to know that the AOA measurements disagree, but it is also necessary to detect which measurement is erroneous. With three sensors, if a single one fails and disagrees with the other two, you can shut off the failed sensor and continue flying as if nothing happened. Of course, the airplane would not be dispatchable until that failed sensor has been serviced once landed.
Some airplanes (e.g. A220) have four primary AOA sensors. But this is more for dispatch availability (MMEL) than for safety. Note that the A220 has two redundant AOA vanes on-top of the primary AOA sensors (SmartProbes) for Direct Mode operation.

thanks! I'm seeing at least 4 locations (possibly 5), 4 sides of forward fuse and tip of vertical stabilizer.  Any area experiencing turbulence due to relative wind would be the outlier, and programming could accept the closest 3 and average them.


text:
Does thickness of boundary layer rise with AoA?
When increasing the angle of attack, the Cl and adverse pressure gradient rise. Does boundary layer thickness rise as well?
Or has an airfoil with higher Cl a thicker boundary layer?

To make a comparison I would set the condition. So the question would be: "Considering two airfoil with the same geometry and at the same Reynolds number, how would change the BL thickness with increasing AoA?"
Another thing that would make the question more clear would be to consider a definition of the boundary layer thickness, and here I would define it as the displacement thickness (other definition are certainly possible).
Clarified this you have a possible answer to your question in this AIAA SciTech paper.

On the left you see at different AoA the development of the boundary layer displacement thickness at Reynolds 60000 simulated with XFLR software. You can observe the propagation of the LSB bubble upstream with the increase of the angle of attack and this cause an increase of the displacement boundary layer thickness behind the bubble.


text:
What is the meaning of 'stall' in this sentence?
I have no knowledge about aviation. Can somebody tell me what is the meaning of "he ran through a series of stalls" in:

He ran through a series of stalls, killed the engine, and brought the
  plane down to a safe and quiet landing.

Source: Blended Coaching: Skills and Strategies to Support Principal Development

Could it also be engine stalls?

The sentence means the airplane was slowed down (generally) and the nose pulled up until the wing stopped generating lift (stalled) and finally "killed the engine" (typically by reducing the mixture until the engine stops running) and then landed by just gliding down to the airport.  Stalls are not a good thing when low to the ground and maneuvering for a landing, as there is no altitude left to recover, so we practice them to recognize when one is about to occur to avoid them, and to recover quickly at the onset of one.


text:
Is there any version of CFM56 with can combustors?
This lamp is sold online:

They claim it's made from a CFM56 combustion chamber. It looks like a can combustor, and I read everywhere that CFM56 uses an annular combustor.
Is there a version of CFM56 with can combustors?

If yes: is this lamp look like one?
If not: from what engine the body of that lamp would be from?

In short
It's the flame tube of an individual can of a cannular combustor, a mix between can and annular combustors. The can may come from auxiliary power unit turbine or a JT8D powering older Boeing 737 and MD-80 or an . It cannot be from a CFM56, all models use annular combustors.
The three main types of combustors:

Source.
All types are approximately to the same scale, meaning an individual can of a can or a cannular combustor is much smaller than an annular combustor.
The can of the lamp support has interconnectors, pipes used to connect the cans.

Details
Recent Boeing 737 and Airbus A320 can use different engines:

CFM56 models -3B, -5A, -5B, -7B,
IAE V2500,
PW1100G,
LEAP

All have annular combustors, single fuel nozzle (SAC) or dual fuel nozzle (DAC) for NOx reduction. However older versions of Boeing 737, -100 and -200,  used a JT8D engine with 8 cannular combustors, the beast you got. In cannular type, the individual combustion zones share a common annulus casing:

Source.
Detail of a combustor:

Source.
The part making the lamp support is the flame tube (liner) of the combustor. The external air casing has been removed. I wasn't able to identify the exact version of the combustor, there has been multiple improvements over time on the JT8D, a famous engine, still used today.
More information about turbofans (pdf).


text:
How to clean up CA1000 corrosion inhibitive compound?
I am working on one of the aircraft parts covered in CA1000 corrosion inhibiting compound that needs to be cleaned and reapplied. I looked at their website and it says it is "a one-part, epoxy capped, PERMAPOL® polysulfide compound".
I have tried using parts cleaner (kerosene-based) and workshop solvent (Naphtha) to clean it with no success. Just wondering if anyone knows how to clean it.

Why not contact the manufacturer and ask them?

Mastinox is formulated to be resistant to fuels, so you wouldn't expect Naptha or kerosene to work in the first place.
Suggest you try denatured alchohol, isopropyl alcohol, or acetone.

This product sounds very similar similar to PRC Pro-Seal, which is also a polysulfide sealant that never becomes fully solid and is very resistant to pretty much any solvent or fuel. If this is the case, you should try heating it with a hot air dryer such as is used to shrink shrink-tube material. Heating it should soften it enough to allow it to be scraped off with a spatula.


text:
How does the wing-tail interaction reduce drag at supersonic speed?
NASA report: "Effects of wing and tail location on the aerodynamic characteristics of an airplane for Mach numbers from 0.25 to 4.63" states that the drag coefficient at zero lift ($C_{d_0}$) is lower when the horizontal tail is close to the wing's trailing edge than when there is no horizontal tail:

An interesting effect of the tail on the drag characteristicsdoes occur. Although the addition of the tail in either the mid- or aft-axial positions causes an increase in CD.o, the forward tail position results in CD,o values slightly less than those for _he tail-off case. This drag reduction occurs since the forward tail is immediately aft of the wing and results in a decrease in wing trailing-edge drag as well as tail leading-edge drag. This reduction in drag coupled with the increased lift results in the forward coplanar tail configuration having the highest values of maximum L/D.

The reason for this drag reduction is that when the horizontal tail is close to the trailing edge of the wing, the trailing edge of the wing reduces the drag of the leading edge of the horizontal tail, and the leading edge of the horizontal tail reduces the drag of the trailing edge of the wing.
Since the $C_{d_0}$ at supersonic speed includes wave, friction, and pressure drag, how does this mutual effect of horizontal tail and wing on each other happen?
From the same document:

One might compare results to a pure delta, or perhaps a reverse swept trailing edge.

@RobertDiGiovanni no the whole report is just about that two configurations compared to horizontal tail off

Identifying the technical report would be great.  Also, it would be good to know the Mach number tested.  Are the leading edges of this configuration supersonic or subsonic at the test condition?  If they are supersonic, one might observe that the merged wing acts as a single wing and only has one set of shocks at the LE/TE vs. the split configuration has two sets.  Another thing to observe is that clearly the area distribution of the split configuration is worse and it will have higher wave drag.

@RobMcDonald https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://ntrs.nasa.gov/api/citations/19930089737/downloads/19930089737.pdf&ved=2ahUKEwjiz-OBgI2JAxWEFlkFHTkNF5IQFnoECBEQAQ&usg=AOvVaw2BbTCCMt-9PNZg9TsyY-Bd

The images you posted are not in the document you linked to.

@RobMcDonald https://ntrs.nasa.gov/citations/19830013883

@sophit https://ntrs.nasa.gov/citations/19830013883

@alireza Thanks for the link.  Interestingly, the wing airfoil has a blunt TE, which can't be pretty, but probably sets up the horizontal tail well.  It looks like this could be explained either by area rule or sets of shocks approaches.  Interestingly, the drag benefit seems to occur across all Mach numbers.

Yes, i presume you're wondering why there can be lower drag with the tail on.  Did it occur to you that a reverse sweep on the trailing edge (of tail forward and/or solid one piece) may produce even less drag?

It would be nice to have those experiments backed up by CFD simulations in order to actually see how the airflow looks like but I suppose that what is at work there is quite simply the area-ruling: the configuration with the tailplane attached to the wing has a sectional area better distributed than the configuration with an aft tailplane and therefore a lower wave drag.


text:
What is this Lockheed Martin plane?

It's on a Lockheed Martin banner showcasing the company's iconic planes. The plane to the left on a crimson background is the U2, and the plane to the right on a blue & tan background is the C130.
It looks like a prototype UAS.

I've seen artist impression of this thing before, possibly even a model. If memory serves, it's a concept UCAV for the US Navy.

Lockheed Martin Sabre Warrior UCAV (concept):

Source

Source
From Defence Forum India:

The Sabre Warrior drone is 46 feet long, with a 36-foot wingspan,
  capable of taking off with 30,000 pounds of load using a 22,000-pound
  trust afterburning turbofan engine. It has two modular payload
  sections, which can be changed by soldiers in the field. Each bay can
  handle one 2,000 pound or two AIM-120 AMRAAM missiles or 10 smart
  bombs or sensors, or even fuel for extended range missions—”even
  while this thing is air refuelable.
Its twin nose can also hold multiple sensors, which are
  interchangeable. And it is designed so there could be a version with a
  cockpit, so they can send man version as an on-the-scene controller,
  overlooking over the unmanned versions.

The Raptor F-22 is a 5th generation fighter, Sabre Warrior the 6th.
Requirements worked with DARPA and USAF.
It has been considered for the UK Future Offensive Air System (FOAS), cancelled in 2005.
More on Youtube.

Looks like something from a sci-fi movie. Very neat.

I fully expected the answer to be, "it is concept nonsense."  Good answer.  Thank you.


text:
How does ATC handle tv coverage of police pursuits in the US?
On YouTube there's a lot of aerial footage of US police pursuits to be found, usually filmed from news helicopters, flying around and doing a lot of maneuvering in the same small area, sometimes in the immediate vicinity of big airports.
Almost always there are more helicopters involved: Police and tv stations, you can sometimes see them crossing the camera view. And all of this time, essentially no one knows where things are going. The whole thing seems to me quite hazardous from an aviation point of view, maybe even more so than the proceedings on the ground.
How are these operations kept safe? Under what rules or procedures does ATC handle this kind of situations?

Most of the video I recall are from the US, so I'd restrict this to that jurisdiction. I don't think I ever seen a "chase video" from Europe.

@Federico You're right, edited. In The Netherlands where I'm located these situations would probably lead to a government crisis...

@Federico I can't speak for other countries, but you occasionally get airborne footage from police helecopters here in the UK.  You don't get News helicopters chasing off after pursuits though.

Under VFR pilots are responsible for their own separation

I fly daily between two small G.A. towered airports in the Los Angeles basin.  There's often police and news helicopter activity within the Class D areas.  The pilots stay in contact with the tower controller and explain where they'd like to go, and ATC generally approves, while coordinating with arriving and departing traffic.
In particular the approach to runway 25 at Hawthorne runs parallel to a major freeway.  Occasionally there have been police and news helicopters operating up and down that freeway, right along final approach.  The tower controller points them out to me as I'm approaching, and if I can call them in sight I'll just maneuver visually as necessary to avoid them.  If I don't see them, they'll usually ask the helicopter to move, though I imagine if it were an urgent police situation I could be told to go around instead.  Another technique they'll use is to tell the helicopter traffic to stay north of the highway and the fixed-wing traffic to stay south of it.  That way you can be pretty close but still not have a collision hazard as long as everyone is paying attention.

I know about the operations of police in South Pacific Area so I will answer from that point of view not the USA as is queried.
The Air Traffic Controllers have an agreement set up between the various Police Forces and themselves. This agreement allows them to operate in a covert capacity if required. When they do this special phrases and/or special call signs are used to give them higher priority.
When something like a chase or surveillance is being carried out the police helicopters are usually operating below the control steps. If not they will talking with ATC to obtain a clearance for either to operate in an area or for particular headings. I have seen clearances be issued that say Stay North of Road X Operate Below 1500 AGL.
If Police operations bring them near an airport, the Terminal Area Controllers or Tower Controllers will separate them from the other traffic. In fact this is very safe operations.
As to do with TV helicopters they have to follow the same rules as all the other helicopters. If in controlled airspace obtain a clearance and if not operate VFR under the VFR Rules. The TV choppers would be told to get lost if they were interfering with Police choppers (Yes I have heard it happen).

Are those police in terminal areas VFR or Special VFR?

Police will operate usually VFR but will upgrade to IFR in terminal area or if weather is marginal

I forgot that in the US you use more airspace classes so you do provide separation even to VFR.

authors: Vladimir F Героям слава


text:
Why do some airplanes allow separate right and left rudder pedal adjustment?
Ideally, when a pilot adjusts the rudder pedals both pedals should move together, to have equal leg length for the left and right legs.
Some aircraft like the Dornier 228 have rudder pedal adjustments where you have to adjust the left and right rudder pedals separately. What is the logic of having provision for separate adjustment of the left and right leg length to reach rudder pedals?

Because not everyone has legs of equal length.

The King Air also has separate adjustment for each pedal. In my examination of that system, I believe the primary reason is simplicity: the individual adjustment system on each pedal is simple and lightweight, whereas a system to adjust both pedals simultaneously would likely be heavier and more complex. Weight and complexity are both undesirable characteristics in aircraft design.

@JonathanWalters I agree, and I think that's answer-worthy.

It's like some stereo amplifiers have two volume controls, while others have one volume and a balance knob. The latter is more logical for the user, but the former is trivial to implement.

As with any question along these lines—"Why did the designers do X"—a definitive answer is very difficult absent specific documentation, which is rare.
I am not familiar with the Dornier 228, but I am familiar with the King Air B200, which is a very similar class of aircraft. Beechcraft also designed the King Air with individual pedal adjustment.
In my examination of that system, I believe the primary reason is simplicity: the individual adjustment system on each pedal is simple and lightweight, whereas a system to adjust both pedals simultaneously would likely be heavier and more complex. Weight and complexity are both undesirable characteristics in aircraft design.
See this excerpt from the King Air B200 Illustrated Parts Catalogue (IPC) depicting the left hand side rudder pedal assemblies:

Source: KA B200 IPC 27-20-00-06
I have highlighted the rudder pedal adjustment lever assemblies—B and C—in light blue. I have highlighted the adjustment pin—No. 375—in green. (Note that the IPC incorrectly depicts the two adjustment levers in reversed locations; see the aircraft photo below.)
The figure clearly shows the simplicity of the design and the way the adjustment relates to the overall rudder pedal control system. The adjustment lever is a simple assembly of stamped metal and hardware, light and cheap to manufacture. The system is simple and intuitive to use and requires little or no rigging.
This is a photo of the left hand side rudder pedal assembly in an actual King Air B200; adjustment is accomplished by depressing the lever with the outer edge of one's shoe and moving the pedal forward or aft:

Any design allowing simultaneous dual adjustment through a single adjustment action would likely have resulted in some combination of increased complexity, expense, weight, or maintenance requirements.
Moreover the system, as designed, allows for separate adjustment, which could be helpful for some individuals or situations.


text:
What is this old US Air Force plane?
What model of plane is visible in this image?

Where is the aircraft in the picture located?

@nexus_2006 probably Kelly AFB. It was on display there for years (1957-2004).  Sadly, I didn't go see it in time.

The early versions of the B36 had 6 pusher propellers. Later versions added a pod with 2 jet engines on each wing. This led to the phrase "6 turning, 4 burning".

Based on the unique 6x pusher-prop configuration, this looks like a derivative of the Convair B-36 Peacemaker. Looking up the Wikipedia article for the B-36 and scrolling down to the variants section, this seems like an XC-99 (or, more aptly, the XC-99):

Public domain image via United States Air Force - USAF photo via, Joaobsen, Wagner, Greer (1980), B-36 Peacemaker in action - Aircraft No. 42, Squadron/Signal Publications; 1st edition, ISBN-10: 0897471016
This was to be a passenger variant of the airframe, with a passenger capacity of up to 400 people. Beyond the prototype, it didn't enter service.

Interestingly, the B-36 was involved in the first Broken Arrow incident where three of its six piston engines caught fire off the coast of British Columbia.

"seems like  ̶a̶n̶ the XC-99:"  ...ftfy ;)

@coconaut if you're interested in other B-36 trivia, there was also a variant, the NB-36H, powered by a nuclear generator which was supposed to combine the endurance of a nuclear submarine with the airworthiness of something that's distinctly not a nuclear submarine.

When I was a boy in Sacramento, CA circa 1955, a C-99 regularly came into McClellan AFB.

XC-99, o e was built and was on display for years at Kelly AFB, Texas and later moved to the Air Force Museum.

This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review

@RalphJ The information in this answer is correct and does provide an answer to the question. The only problem is it doesn't provide info that wasn't in the other answer already.


text:
How do propeller planes sync their propellers?
While reading this question, I found that the answers did not address the point I had come for.  On planes with electronic propeller synchronization, how is it actually accomplished?  I know why propeller synchronization is useful but I am curious about the mechanisms behind how it works.

Consider finding some way to update the existing question to bump it up to the top of stack and emphasize that you are interested in the actual mechanism?  Oops I assumed it was your own question, guess it wasn't.  Still, it seems like your question is pretty much a duplicate, not sure what's the best thing to do here.

You could offer a bounty--

You could just edit line 2 to say something like "How is it achieved?  I.e., what is the actual mechanism?"  Then leave a comment to emphasize that this part of the question has not yet been answered.

Or if no one objects and votes to close, maybe just leave your question up and maybe you'll get the answers you are looking for.

@quietflyer I don't think it is a duplicate at all. The other question only asks what prop sync is and how it is used from a pilot perspective. It does not ask about the actual mechanism behind it.

@quietflyer "How is it achieved?" -> You synchronize RPM of the engines. But it does not ask about how that synchronization works from a technical perspective.

@Bianfable so you are saying "by synchronizing the engines" is a sufficient answer to line 2, "How is the synchronization of the props achieved?"  Or vice versa, if line 2 is interpreted to read "How is synchronization of the engines achieved", then a sufficient answer is "by synchronizing the props"?  The original question was obviously asking for more than that and I don't see how the present question is not a duplicate.  After all, similar terse answers would seem to be equally suited (or unsuited) to the present question as well.  But, I'll save my close votes for something else...

I don't think this is a dupe.  The solution isn't just to sync the RPM's, but also to get blades in the right relative phase, which requires more than just matching RPM.  (The C-130 engines ran at 100% RPM the whole time, but blade position mattered, a lot.) VTLO.

@RalphJ That sounds like a great answer in the making!  That is the type of stuff I want to know.

Does this answer your question? What is propeller / engine sync and how does it work?

@SSumner Other comments and the question explain why this is not a dupe.

@ymb1 Hate to see that good answer wasted.  Hope you consider re-posting it if is still applicable once the question is stabilized, as long as community consensus is that question is not a duplicate.  Also, why not post it to the older question too, it sure seems applicable there.  Don't think there is any rule against posting the same answer to two questions.

Is the point of some of the comments meant to be that "prop synchronization" inherently implies synchronization of the propeller blade positions, not just engine rpm?  Wikipedia calls that function a "synchrophaser". ( https://en.wikipedia.org/wiki/Propeller_synchronization )   A question that is specific to how that works would arguably not be a duplicate.

I fly a large 4-engine turboprop.  It uses constant speed hydraulic props, which automatically change blade angle to maintain 1020 rpm.  The sync box (which I was unable to find a picture of) takes inputs from each engine's tachometer generator (where it gets the RPM signal) and a pulse generator, which is a magnetic pickup right behind the prop.  There is a magnet on the number 1 blade of each prop.  With this information, the solid state logic components inside the sync box can slightly change blade angle by sending power to the speed derivative servomotor.  This is different from the answer that @davidinnes provided, but I suspect that he's correct for the type of propellers he's familiar with.  The sync system on the P-3 also takes inputs through a potentiometer attached to the power levers, and can start increasing or decreasing blade angles if you change your power setting quickly.  It works faster than the hydromechanical system and lessens RPM overshoots and undershoots as the prop works to get back to 100% rpm.

In this picture you can see syncrophasing in action.  The props are all slightly out of phase with each other, which reduces noise and vibration. #2 and 4 look pretty close, but it's far from a perfect system.  You can definitely tell the difference from the cockpit when it's working well.  Again as @davidinnes mentioned, you can adjust the system to the change where the point of minimum (or maximum) noise is in the cabin.  We call it "running the buzz" up and down the tube, and it's a great way to annoy a navigator that you don't like

By modulating the fuel flow to the slave engine, ie the one which is to synchronise to the "master" engine, Note. Limited authority of fuel modulation and not permitted in Take off or approach.
One writer alluded to synchrophasing to not only reduce beating bit alos reduce noise, You can as I have done move the point of minimum noise around/along the cabin by small changes in phase angle. Actual angle (relative position of the prop blades) depends on number of blades per engine, Easy with two engines, more than 2 ,,, its more of an art

Might as well post that answer here too, as it addresses line 2 -- https://aviation.stackexchange.com/questions/14263/what-is-propeller-engine-sync-and-how-does-it-work

I've been told that the flight engineer's position in a B-17 was such that he could look out a window and shine a strobe light at the prop blades on one side of the plane. The strobe was slaved to one of the engines and the engineer could use the strobe light to tweak all the other engines into sync manually.


text:
What was this helicopter doing?
I recently saw a helicopter with the registration "N61NR" flying repetitive patterns back and forth over my house and from my observations, it appears that it was landing in a grass field near a school and that it proceeds to fly directly towards the nearest hospital with appropriate round trip times (I know this because I regularly see medical helicopters flying that way).  Any ideas, flight maps, or general commentary about the helicopter itself?  It has repeated this cycle 10+ times.

Training for pilots/crews? Its difficult to say without knowing. Can you verify that N number? It says that it is an invalid number on the FAA site. N61NR is a Bell 206 registered to "SWOPE AVIATION LLC".

I'm pretty sure that was it but I will look more closely next time it comes by...

ok, could be a 1 instead of an I, I suppose...  any more about that helicopter?

No, "Swope Aviation" doesn't seem to have a website or other online presence. The registered address seems to share a building (or very close address with) Swope Construction.

yes, it is a 1, not an "I"

@RonBeyer can you give me a link to the FAA page?

Here is the link for the N-Number Inquiry form where you can type in the N-Number (without the "N") to get registration details.

The aircraft N61NR is registered to "Swope Aviation LLC" as per the FAA N-Number Inquiry Site:

(Source: FAA N-Number Inquiry)
Doing a little more research, the business located near the address in the helicopter registry is Swope Construction.
Without knowing more details it is difficult to say what this particular helicopter is doing. The flight is not being tracked on FlightAware as far as I can search. The helicopter's last recorded flight in FlightAware was over a year ago.
Anything I say is going to be pure guesswork, the helicopter could be leased to a crew for training, they could be checking routes, or doing some kind of survey work. Swope Aviation LLC does not have a dedicated website or online presence. If you are concerned about the operations that the flight is conducting regarding the safety to the aircraft or people on the ground, you can always contact the FAA to report the activity and they will investigate.

Since it is landing so close to one of Swope Construction's sites, I would assume that it is doing something related to that.  Thanks for the great work!

Swope Construction, same address. Current and past projects. True aviation lover: "Chandler Swope founded Swope Construction and is also a helicopter pilot. He has piloted WVVA photographers shooting aerial video for the past 25 years.". Good story about WV11, at Swope farm.

Nice find @mins

@mins And the Google Fu master demonstrates his prowess yet again. Teach us sensei. [bows]

It's interesting that a question closed as "too broad" comes up with detailed information mostly based off the tail number and some dudes on the internet. :)  Good job.


text:
Do we fly full size aircraft with video game style joysticks?
Are there planes with electronic joysticks as shown below?

RC airplanes are incredibly effective at using this technique. For actual planes it would remove the need for rudder pedals and a stick along with potentially being easier to get used to.
Are thumb controlled sticks used in aviation? or is there a reason to why they aren't used?

This is not a great answer, but I think if I sat as a passenger on an RC plane or in a flight simulator cabin, I would get very sick, very quickly. There's a reason people pay a lot of money for large, realistic controls: it gives you much more precision and control than a tiny game pad.

There are a lot of planes that have electronic (aka fly-by-wire) joysticks (aka side-sticks). RC Planes (at least ones with similar control surfaces) use two joysticks, which would be much more difficult in a full scale aircraft.

Suggest you look into the Airbus A320 series to answer your question.

I'm not sure I understand the question.  Is it about the configuration of the controls or electronic vs cable connections?

Plenty of aircraft use 'joysticks' (this one even uses two), so perhaps it would help to explain what the twin sticks would control? I'm not familiar with RC aircraft, so how do two sticks control three axes of movement, plus thrust? If you explain a little more about exactly how your idea would work then you may get better answers.

@Pondlife In my experience, the left RC joystick is for pitch/roll while the right joystick is for throttle (Y axis) and rudder (X axis).

I am aware that side sticks exist but that is not what I am asking, I am asking if it would be better to control everything with your thumbs where you can use both thumbs to control everything and remove the need for rudder pedals

"Better"  NO!  Why would you deprive yourself of additional channels for control inputs?  If you fly in three dimensions, and have three axis of rotation, it makes sense to have three channels of input.  Prevents mode confusion.  (OK, the RAH 66 Comanche did that, but it was on a joystick as well).  Ergonomics is a fascinating science, but it's a whole art form that most of us exploit without always knowing how many tests went into getting it to "feel right" as a man-machine interface.  (And don't get me started on the Yoke versus Stick debate ...)

Since I don't have pedals for my flight sim my joystick controls rudder by twisting it. It's really awkward btw.

For some reason this question is reminding me of this scene from MiB

@dalearn Terminology alert! This is a joystick and this is a game controller. The latter can contain one or two thumb-operated mini-sticks.

Apart from cheap gaming joysticks often having a low quality, I don't see a big difference between a gaming joystick and a plane joystick. What exactly are you talking about?

as @CodesInChaos says, this question seems fundamentally somewhat confused.

I am talking about a controller similar to one used to control an RC plane and why that would/would not work on a real plane.

OT: Flying RC aircraft with just the thumbs is wrong. You fly them with two fingers on the controls: the index finger and the thumb. This allows for much finer movements.

hmm...  I might have to try that sometime!  I always use my thumbs to  control things and I can successfully fly habu's but my movements are not smooth!

As others already said, joysticks are used. But there is a fundamental difference with the RC controls.
We humans do much better job of dynamic control when controlling the force rather than position/displacement. It is too long a discussion why, but the main reason is that we have special force feedback sensors in our muscles. (Yes, it's a common misconception that we have only five senses).
For this reason, airplanes are generally controlled by force. Even those that have mechanical links and deflect the controls proportionally to position; even those FBW that measure position of the controls (the first type that Peter Kämpf mentioned) - they still, in the end, are controlled by human force. This is why correct loading (spring or otherwise) is crucial: certain displacement requires certain muscle force, and this force we apply and control.
Ideally, you want to tune the loading so that a certain force would produce a certain desired end effect. Say, each 1 kg pull produces additional 0.1g of normal acceleration. This naturally happens with classic reversible controls: when airspeed increases, the required control deflection (for a given acceleration) decreases significantly. But the required force per unit of deflection increases by the same amount. Thus we have constant force per acceleration, despite having very different control travel. This travel difference can be an order of magnitude, but it poses no problem for the pilot, because force is the same. In fact, pilots use it as a secondary feedback about airspeed.
Electronic (FBW, fly-by-wire) joysticks could be made to require no or little force, like RC controls, but this is never done. A great deal of effort is invested in producing optimal loading. For one, an accidental move of a light control might destroy the airplane. (This may happen even with RC airplanes, which are much stronger relatively). But even more importantly, it has been proven that gradual precise force control works better for us that position control.
This is why some aircraft (starting from F-16) moved away from positioning entirely and measure force on the stick directly. However, this just doesn't feel natural for us: we expect some movement in response to a force; so a small amount of movement is generally allowed even for pure force control.
The amount of travel also matters, but this is only a secondary feedback. Besides, it works better when we see the movement, which doesn't always happen when flying.
When you press brake in your car, you also feel and coordinate mainly the force on the pedal rather than its position. This allows you to adapt to different cars quickly. Racing cars have very little pedal travel. But if the required brake force was very light, you wouldn't be able to brake smoothly, no matter what travel there was.
Now the RC controls have almost insignificant spring, and are actually controlled by position. Normally, this doesn't give a precision anywhere near what a real airplane would require. As Daniel noted in his comment, you wouldn't be a happy passenger on such an airplane. This is partly mitigated by using a very close position reference (the hands grab the sides of the control) and using our most sensitive fingers, but still only partly.

This addresses some of the ergonomic issues that I'm not too good at explaining.  Nicely said.

Most competition RC pilots fly with very stiff springs because they need to "feel" the aircraft flying. I'm not a competitive pilot but I always tighten my springs to max for the same reason (though I don't splurge on replacement springs). There's a saying in RC - soft springs sells radios, stiff springs wins competitions.

They are used, they are just bigger joy sticks than used for RC flying.
A current example is the Airbus A320 (and related family) of passenger aircraft.  A short video of the joystick in action(called "side stick", start at about 1 minute in).  There is no direct mechanical linkage between the stick and the flight controls.

(For the A330, but basically the same).
For more detail, you can download this (slightly out of date, but with enough information to be useful) Flight Controls lesson for the A320 here.

I am more curious about thumb controlled flying as you could control
  everything from what essentially looks like a video game controller.

@Rory Alsop noted that ...

... even video game controllers are terrible for this. The bigger the stick the better fine control you have over it. This is why for flight
  sims for PC's and consoles, keen players buy proper joysticks -
  otherwise they are twitchy and hard to handle

Video game controllers require two hands, have poor sensory feedback (as compared to a stick type controller) and are not as ergonomically effective as a multi-axis stick.  Also, there are some "push buttons" on a control stick that allow moving a finger or a thumb to activate other functions, like the "take control" button in the side stick(For swapping control between left seat and right seat pilots).  On some sticks you'll also have the "push to talk button" for the radio, as has been done for decades.  It's an efficient use of the hand, without having to move the hand for multiple tasks.

This makes me wonder how hard it'd be to get an Airbus sidestick to work with your PC...

@UnrecognizedFallingObject it wouldn't be plug and play, and it'll be a completely custom job because nobody gets controls from a real plane and attach it to a PC.  But since it is all electronic based, it's just matter of translating all the actions to PC understandable code.

@Nelson -- I suspect somebody building a A320 sim's probably done it before, at least...

@Nelson here is one example http://www.a320homecockpit.de/00000096221175917/00000096330b5e512/00000097c213ac506/index.html

@daelarn Another important thing is sensory feedback, which in turn helps with fine control. Something that's very sadly missing from most videogame controllers.

@Shadur I folded that point in about sensory feedback.

A thumb operated joystick requires fine motor skills while a big lever on the same joystick (essentially the modern control device as answered by KorvinStarmast) provides the same functionality but with larger movements required to make them. This is helpful for subtle control work and makes piloting in turbulence feasible, something RC flyers don't really have to contend with while standing on the ground.

Not so. When your plane weighs 1.3oz, everything is turbulence ! The small thumb sticks on rc aircraft are better due to the very quick movements needed from one axis extreme to the other, as opposed to a stick on a real aircraft.

@Sirex: the point is that the pilot's hands are not shaken by the turbulence the aircraft experiences, because the pilot is always standing on solid ground.  I initially interpreted it the same way as you, so an edit might help.

ah. fair enough.

Thumb controlled? No, this would be impossible in a moving aircraft. For precise input, pilots need to rest their forearm on an armrest while handling their joysticks. Due to their location at the side of the pilot's seat they are called side sticks. There are even two different types:

Airbus-type side sticks work against springs and can be pivoted fore-aft for pitch rate and left-right for roll rate. Depending on the active control law, the motion can also code for elevator and aileron deflection angle (direct law).
F-16 type side sticks are immovable, but sense the force which the pilot uses for control. The early models of the F-16 used side sticks with no free movement at all, which caused an awkward feeling, so more recent models allow for some motion. But it still needs a lot of force to move the stick, and the full range of motion is just a few millimetres.

F-16 control stick (picture source). Due to the complexity of the system which they control they have a lot more buttons and switches than your average joystick, but in principle they are the same.

It's the other way around, we play video games with aircraft style joysticks.
The games industry looked at aircraft and basically took those designs as inspiration for their products, in no small part because a lot of those games were about controlling flying aircraft and spacecraft and it'd be more immersive to have controls looking (somewhat) like the real thing.

Of course there is a massive variety of joysticks out there, but the most serious ones aimed at high end gamers still look like modern day fighter sticks to this day.

Interesting. Do you any source about that?

@Taladris Simply goggling for images of "realistic joystick" gives you instant hits. The most conspicuous example is Thrustmaster HOTAS Warthog, modelled on the A-10 flight controls. Thrustmaster's previous high-end product was the HOTAS Cougar, modelled on the F-16's flight controls. And if you look at other high-end joysticks that are not imitations but still high-end sticks - such as the Saitek X-52 - you can see many similarities between them and real life HOTAS systems.

Please add some of those Comments to the answer since examples usually help to illustrate a point.

I think the other answers are missing something.  I think the OP is asking about a single control input, rather than having a joystick (or wheel) to control ailerons & elevator, and foot pedals to control the rudder.  Perhaps with some linkage to automatically maintain coordination, like IIRC the Ercoupe.
One reason is that in light aircraft at least (I have no experience with commercial) you sometimes want NOT to be coordinated, as for instance when you're doing a sideslip to lose altitude/airspeed for a short field landing.

well, generally on an RC radio such as the one I posted a picture of, pushing the left stick up is throttle and side to side is rudder and the left stick up/down is elevator and side to side is ailerons.

the switches at the top control gear, flaps, optional thrust vectoring on/off on some planes, mixing flaps/ailerons for technical maneuvers using flaperons, lights, and sometimes a camera or other function such as a drop chute or streamer

@dalearn: There's also the fact that the controls in most light aircraft work through physical cables connecting the controls to the control surfaces, so there's direct force feedback.  In addition, most light aircraft were designed and built before electronic controls became cheap, lightweight, and reliable enough for general use.  I still have the original radio out of my Cherokee sitting in the shed: it has vacuum tubes.

Joy sticks and control yokes are traditional for full size aircraft for very functional reasons going back to the dawn of flight.  All of the pre-WWII aircraft were controlled by direct mechanical linkage. the is moving the stick or control column for and aft pulled on cable that moved the elevator up and down.   Moving the stick or wheel (yoke) side to side caused one aileron to go up and the other down. The ruder pedals were on a toggle or t bar connected to the rudder cables and directly moved the rudder left and right. The larger the plane the larger and more stressful the movements were as the aerodynamic forces on the controls (back pressure) increases with the aircraft's size and speed. This is the original reason multi engine bombers and cargo planes started having co-pilots.  In bad weather it might take the strength of 2 men to handle the controls. By WWII planes were so large and fast that hydraulically boosted controls were needed.  Think of these like the power steering or brakes on your car. Large movements were needed to open and close the valves and allow the hydraulic fluid to flow and move the controls. The first production aircraft that did not have a mechanical connection between the pilot ant the control surfaces was the General Dynamics F-16 (1979 - present).  The F-16 is a side stick "fly by wire" design were the pilot tells the computer what he wants to do, and the quad redundant digital computers figure out what control surfaces need to move to achieve this.  It also prevents maneuvers that would exceed certain safety parameters.  Since planes are durable and stay in service for decades, familiar patterns of instrumentation and controls last for decades with few changes.


text:
Why did WWII prop aircraft have colored prop tips?
Why do propeller aircraft from World War II and similar planes sometimes have the tips of the props colored? I see it on single engine planes like the P-51 as well as bigger, multi-engine planes such as the B-17.

Actually, the larger planes very often did have differently coloured prop tips. It's possible that they don't show up very well in black and white but, if you look at wartime colour photography, you can often see them. For example, all of the planes in this article have coloured prop tips (the last five photos are modern, but the rest are from WWII).

Prop slap hurts

You'll also tend to find that early war aircraft (like these early B-17's in the photo, the side gunner positions showing they're relatively early war) didn't always have painted tips, in part because in the earlier stages of the war there was less time/thought put into those things. Battle of Britain Hurricanes/Spitfires, for example, often didn't have painted tips either

@ymb1 Indeed, restorations typically have safety stripes or colored tips. For example Fifi (the B-29) has safety-yellow tips, as do many of the surviving B-29s.

Semi-related I did this on the cooling fan for my car's engine, to increase visibility while working in the engine bay with the motor running.

That is not unique to WW2 planes, this is fairly common on most prop planes. It is to increase the visibility of a running (spinning) propeller to help people on the ground from accidentally coming in contact with them. The unpainted propellers on the large aircraft may be more related to wartime haste than anything else.

(source)
From the Mccauley propellor guide

7. Why are propellers painted?
The faces of the propeller blades toward the pilot are painted non-reflective black so the spinning
  propeller is not seen as a shiny, hypnotic disc. The tips on the
  opposite side are painted bright colors so the spinning propeller can
  be more easily seen to warn those on the ground about walking into it.

Have there been any studies that show that paint would be seen more?

@user6035379 The point isn't just to see the prop, its to see the prop tips. The tips are hard to see, the prop itself isn't, but because the tips move much faster than the inner parts, they aren't as clear. It helps you identify the diameter of the prop when near a running engine (although you shouldn't be anywhere near a running prop engine anyway).

@user6035379, there probably have been studies, but it's pretty obvious in direct observations...  One can not easily see the spinning propeller's "disc", but can very easily see the "circle of death" created by the painted tips.

I also did some hunting and it appears there is no actual regulation requiring it here in the US under the FAA currently but it is common practice.

The prop tips are painted for visibility, to show that the prop is turning. This is especially important when the aircraft engine will be running in close proximity to people on the ground, but is also helpful in alerting the crew of other aircraft that the engine is running, and the aircraft might be moving soon.
For visibility, the tip color should be in high contrast to the blade, typically white on black.
Some operators paint the prop tips in an alternating pattern for a strobe effect for heightened visibility. This is especially helpful when operating in areas where people on the ground may be unused to being around aircraft; the strobe effect is an attention-getter. A three bladed prop painted in this way might use a pattern of one, two, and three stripes, or two, three, and four stripes.
Here is an example of what this pattern would look like on a 206:

Source: own work
This is what the pattern on a Quest Kodiak looks like in motion:

Source: excerpt from original photo by Dave Forney

Visibility. Even on modern aircraft. On the flight decks of carriers for example. The E-2C and C-2A's prop tips are painted with a unique paint. As the prop turns, the friction between the prop and the air cause the paint to glow making it easier to see.

The aerospace and automotive-grade paint is applied to the tips of aircraft propeller blades, helicopter main and tail rotors, and other rotating objects to allow personnel to avoid injury or death from coming into contact with them in low-light situations.
The paint was developed under a Naval Air Systems Command (NAVAIR) contract as part of the Navy’s Small Business Innovation Research (SBIR) program.
—Defense Holdings, Inc.

Source—The [above] un-retouched photos show how a propeller with its blade tips painted with DHi’s PL safety paint (seen as two green rings) compares to a prop painted with traditional red and white safety marking paint (which is nearly invisible).

I don't believe that "glowing paint" is right. Some aircraft like the V-22 Osprey or the CH-46 have tip lights for use when flying in formation, but I can't find any reference to "friction paint". Do you have any source for this?

The after glow website is down for me, but I can't see where it says that it is friction activated? It is photoluminescent, which basically means "glow in the dark" and is emitting stored light energy.

The FAQ refers to 'charging' the paint with UV (including sunlight) then expecting 8+ hours of glow.

As mentioned above, the bright paint is there to make it easier for ground personnel to spot the edges of the propeller arc in daylight operations.  The picture of the early B-17s looks late pre-war, when that was the style for the Air Corps.  Later example from the war do add this hi-viz paint to the tips of props.  I guess there were enough accidents associated with propellers that it became imperative to paint props this way for safety reasons.

It's not limited to WW II era airplanes.  Just about all propellers used today use this hi-viz paint on the tips, like the current production sample of an SR22.


text:
Why do Czech Airlines have the airline code (IATA airline designator) "OK"?
Is there any specific reason why Czech Airlines have OK as the IATA airline designator?
According to an urban legend:

Urban legend says that when airline names were awarded -- I believe in 1946/46 -- the Czechoslovak delegation, not versed too much in English, just said OK to the questions asked. So the name stuck.

I do not much believe in the legend, but still the question remains.
I would expect that at the time when the (then) Czechoslovak Airlines were assigned the code, there were not so many airline operators as nowadays and that CS (or something similar) must have been available.

It starts with the International Telecommunications Union, which assigned radio call sign prefixes for each country in 1927. The OK prefix was assigned to Czechoslovakia. Other than the largest countries (US, USSR, UK, France, etc.) there seems to be no specific pattern to the assignments. When ICAO assigned aircraft registration prefixes for each country it usually based them on the ITU prefixes. In 1947, when ICAO assigned 2-digit airline identifiers they chose to use the country’s registration prefix for Czechoslovakia’s flag carrier. IATA originally based their airline ID’s on ICAO’s 2-letter ID’s. In 1982 ICAO changed to their current 3-letter format.

IATA codes don't always bear much relationship to the airline name...
AF for Air France and AA for American Airlines make sense. But then there is Spirit Airlines = NK, JetBlue = B6, go figure.  Also, "CS" right now is Continental Micronesia... again, go figure.

Federal Express had to accept FM initially. When FX became available they grabbed it. FM was then assigned to Lufthansa Cargo as they had a separate AOC from the passenger ops.

@Anilv I’ve always been curious who had FX before. Do you know who it was?

Do you know how the ITU codes were assigned?

Hi TomMcW..refer http://www.avcodes.co.uk/airlcoderes.asp  the main site will give have a box to click if you want to check historical data.

It really comes from the original ICAO designator for aircraft registration in former Czechoslovakia. A more believable "legend" goes that at the ITU conference in Washington in 1927, the Czechoslovakian delegation wanted to be assigned with the code "CS", but that one was already given to Portugal, probably in honor of the King Carlos.
So the Czechoslovakian delegation had to quickly come up with something else. The main Czechoslovakian delegate's name was Otto Kučera... and so they picked his initials O.K. (see the page 28 in this document).
And indeed, they were not stupid and knew that OK sounded cool already back then. So the conference codified it, and since then, all the aircrafts registered in the Czech Republic (and before in Czechoslovakia) use the registration prefix OK.

btw, I just noticed I wrote my answer exactly on the last day of existence of Czech Airlines, 26th October 2024, when CSA had their very last flight after 101 years after they commenced their operations.